In The Airport Murder Case, Mr. Keen is called to investigate the shocking murder of Walter Haskell, who is found stabbed to death in a phone booth at a bustling city airport. The scene is chaotic, with passengers unaware of the crime occurring just yards away. Walter's wife, Emily, is distraught as she recounts the events leading up to her husband's death, emphasizing the urgency of the situation as Walter was about to leave for Europe on a business trip. The police are stumped, having found no clear motive or signs of robbery, which deepens the mystery surrounding his murder.